Added mutex and semaphore modules to demonstrate locks

Added two modules to demonstrate locks.

Mutex demonstrates a simple mutual exclusion lock. Semaphore
demonstrates a semaphore for controlling access to a pool of resources.

The main class of both programs is App.java.

semaphore/src/main/java/com/iluwatar/semaphore/App.java

@@ -0,0 +1,43 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.semaphore;
+
+/**
+ * App.
+ */
+public class App {
+    
+  /**
+   * main method
+   */
+  public static void main(String[] args) {
+    FruitShop shop = new FruitShop();
+    new Customer("Peter", shop).start();
+    new Customer("Paul", shop).start();
+    new Customer("Mary", shop).start();
+    new Customer("John", shop).start();
+    new Customer("Ringo", shop).start();
+    new Customer("George", shop).start();
+  }
+  
+}

semaphore/src/main/java/com/iluwatar/semaphore/Customer.java

@@ -0,0 +1,63 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.semaphore;
+
+/**
+ * Customer.
+ */
+public class Customer extends Thread {
+    
+  private String name;
+  private FruitShop fruitShop;
+  private FruitBowl fruitBowl;
+  
+  /**
+   * Customer constructor
+   */
+  public Customer(String name, FruitShop fruitShop) {
+    this.name = name;
+    this.fruitShop = fruitShop;
+    this.fruitBowl = new FruitBowl();
+  }
+  
+  /**
+   * run method
+   */   
+  public void run() {
+        
+    while (fruitShop.countFruit() > 0) {
+      FruitBowl bowl = fruitShop.takeBowl();
+      Fruit fruit;
+            
+      if (bowl != null && (fruit = bowl.take()) != null) {
+        System.out.println(name + " took an " + fruit);
+        fruitBowl.put(fruit);
+        fruitShop.returnBowl(bowl);
+      }
+    }
+        
+    System.out.println(name + " took " + fruitBowl);
+        
+  }
+    
+}

semaphore/src/main/java/com/iluwatar/semaphore/Fruit.java

@@ -0,0 +1,60 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.semaphore;
+
+/**
+ * Fruit.
+ */
+public class Fruit {
+
+  public static enum FruitType {
+    ORANGE, APPLE, LEMON
+  }
+    
+  private FruitType type;
+    
+  public Fruit(FruitType type) {
+    this.type = type;
+  }
+    
+  public FruitType getType() {
+    return type;
+  }
+  
+  /**
+   * toString method
+   */ 
+  public String toString() {
+    switch (type) {
+      case ORANGE:
+        return "Orange";
+      case APPLE: 
+        return "Apple";
+      case LEMON: 
+        return "Lemon";
+      default: 
+        return "";
+    }
+  }
+
+}

semaphore/src/main/java/com/iluwatar/semaphore/FruitBowl.java

@@ -0,0 +1,78 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.semaphore;
+
+import java.util.ArrayList;
+
+/**
+ * FruitBowl.
+ */
+public class FruitBowl {
+    
+  private ArrayList<Fruit> fruit = new ArrayList<>();
+
+  public int countFruit() {
+    return fruit.size();
+  }
+
+  public void put(Fruit f) {
+    fruit.add(f);
+  }
+  
+  /**
+   * take method
+   */   
+  public Fruit take() {
+    if (fruit.isEmpty()) {
+      return null;
+    } else {
+      return fruit.remove(0);
+    }
+  }
+  
+  /**
+   * toString method
+   */   
+  public String toString() {
+    int apples = 0;
+    int oranges = 0;
+    int lemons = 0;
+        
+    for (Fruit f : fruit) {
+      switch (f.getType()) {
+        case APPLE:
+          apples++;
+          break;
+        case ORANGE:
+          oranges++;
+          break;
+        case LEMON:
+          lemons++;
+          break;
+        default:
+      }
+    }
+        
+    return apples + " Apples, " + oranges + " Oranges, and " + lemons + " Lemons";
+  }
+}

semaphore/src/main/java/com/iluwatar/semaphore/FruitShop.java

@@ -0,0 +1,103 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.semaphore;
+
+/**
+ * FruitShop.
+ */
+public class FruitShop {
+    
+  private FruitBowl[] bowls = {
+    new FruitBowl(),
+    new FruitBowl(),
+    new FruitBowl()
+  };
+    
+  private boolean[] available = {
+    true,
+    true,
+    true
+  };
+    
+  private Semaphore semaphore;
+  
+  /**
+   * FruitShop constructor
+   */
+  public FruitShop() {
+    for (int i = 0; i < 100; i++) {
+      bowls[0].put(new Fruit(Fruit.FruitType.APPLE));
+      bowls[1].put(new Fruit(Fruit.FruitType.ORANGE));
+      bowls[2].put(new Fruit(Fruit.FruitType.LEMON));
+    }
+        
+    semaphore = new Semaphore(3);
+  }
+    
+  public synchronized int countFruit() {
+    return bowls[0].countFruit() + bowls[1].countFruit() + bowls[2].countFruit();
+  }
+  
+  /**
+   * takeBowl method
+   */   
+  public synchronized FruitBowl takeBowl() {
+        
+    FruitBowl bowl = null;
+        
+    try {
+      semaphore.acquire();
+            
+      if (available[0]) {
+        bowl = bowls[0];
+        available[0] = false;
+      } else if (available[1]) {
+        bowl = bowls[1];
+        available[1] = false;
+      } else if (available[2]) {
+        bowl = bowls[2];
+        available[2] = false;
+      }
+            
+    } catch (InterruptedException e) {
+      e.printStackTrace();
+    } finally {
+      semaphore.release();
+    }
+    return bowl;
+  }
+  
+  /**
+   * returnBowl method
+   */   
+  public synchronized void returnBowl(FruitBowl bowl) {
+    if (bowl == bowls[0]) {
+      available[0] = true;
+    } else if (bowl == bowls[1]) {
+      available[1] = true;
+    } else if (bowl == bowls[2]) {
+      available [2] = true;
+    }
+  }
+    
+}

semaphore/src/main/java/com/iluwatar/semaphore/Lock.java

@@ -0,0 +1,34 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.semaphore;
+
+/**
+ * Lock.
+ */
+public interface Lock {
+    
+  void acquire() throws InterruptedException;
+  
+  void release();
+    
+}

semaphore/src/main/java/com/iluwatar/semaphore/Semaphore.java

@@ -0,0 +1,51 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.semaphore;
+
+/**
+ * Semaphore.
+ */
+public class Semaphore implements Lock {
+
+  private int counter;
+    
+  public Semaphore(int counter) {
+    this.counter = counter;    
+  }
+  
+  /**
+   * acquire method
+   */
+  public synchronized void acquire() throws InterruptedException {
+    while (counter == 0) {
+      wait();
+    }
+    counter = counter - 1;
+  }
+  
+  public synchronized void release() {
+    counter = counter + 1;
+    notify();
+  }
+
+}